The present invention refers in general to control surfaces for aircraft, such as elevators, rudders, landing flaps, ailerons, and other similar lifting surfaces.
It is an object of the present invention to provide an optimized structure for an aircraft control surface, in order to reduce the weight of the control surface, thus, reducing fuel consumption.
Additionally, it is also an object of the present invention to provide a control surface for an aircraft which can be easily maintained, and manufactured with a reduced number of components, in order to simplify its assembly and manufacturing process.
Aircraft are provided with different types of movable lifting or control surfaces which are used for maneuvering the aircraft during flight, take-off and landing.
Typically, these control surfaces are formed by panels supported by an internal structure, which is hinged to the aircraft at its leading edge, so that the control surface is pivoted around the hinges by actuators. Due to the large area of some of these controls surfaces, and due to the high speeds that an aircraft like a commercial one reaches during flight, these control surfaces must support high torsion and bending loads.
Elevators are control surfaces placed on both sides of the Horizontal Tail Plane (HTP) of an aircraft, and they are used to control the pitch of the aircraft. Similarly to the case of the torsion box, elevators are mainly multi-rib structures made of composite materials, formed by at least a main spar, and a plurality of ribs supporting upper and lower panels.
Elevators are usually constructed as one assembly although in very large commercial aircraft, they are split in two different sub-assemblies, inboard and outboard elevators. Similarly, in the case of rudders for large aircraft, the same concept is applied to the rudder design, with upper and lower rudders.
FIG. 1 shows a conventional honeycomb panel structure for an elevator which includes a front spar (1) located near the leading edge (5), a rear spar (2) closer to the trailing edge (6), a plurality of ribs (3) joined to the front spar, and upper and lower panels (4,4′) supported by said spars and ribs. The traditional orthogonal arrangement of the ribs with respect to the front spar can be seen in FIG. 1.
The elevator is provided with several hinge fittings (7) at the leading edge (5) for creating a pivoting connection between the elevator and the lateral torsion box of an HTP. Several actuator fittings (8) are also provided at the leading edge for connecting actuators (not shown) such as hydraulic cylinders. The elevator ribs typically have one end joined with an actuator or with a hinge fitting.
Some traditional control surfaces structures are formed by spars and ribs.
FIGS. 2(a) and 2(b) show a known multi-rib architecture for a rudder, formed by two spars (1,2), a set of ribs (3) and cover panels, all of them made of honeycomb sandwiched material, as shown in FIG. 2(b).
Most control surface structures of the prior art are non-monolithic structures, since they are constructed using sandwiched panels formed by a honeycomb core with Carbon Fiber Reinforced Plastic (CFRP) face sheets as surface panels. It is known that honeycomb sandwiched panels are difficult to repair and suffer from water ingestion during flight.
Another known structure for control surfaces, especially for flaps, is the composite multi-spar architecture, which can be an option over traditional multi-rib structures, with the aim of both weight and cost reduction. A multi-spar structure is formed only by spars and cover panels, so that the ribs are replaced by a number of spars longitudinally arranged.